Method of making splined gears



Jan. 27, 1931. E DAVIS METHOD OF MAKING SPLINED GEARS Filed Aug. '7, 1930 WN MN 1 ATTORNEYS i Patented Jan. 27, 1931' UNITED STATES PATENT OFFICE ERNEST F. DAVIS, OF MUNGIE, INDIANA Application filed August 7, 1930. Serial No. 473,647.

The object of my invention is to produce a splined gear having hardened teeth wherein the splined portion is more accurate than has heretofore been considered commercially practical, the production of said gear involving the new and improved method of heat treatment and quenching.

The accompanying drawings illustrate a special carrier and an associated group of gears.

Fig. I being an axial section; and

Fig. 2 a cross-section on line 2-2 of Fig. 1.

My invention contemplates the initial pro duction of gears 10 of unhardened material capable of being hardened by a heating and quenching manipulation and these gears have their splined portions produced by a broaching operation which reduces the splined portions to within a few thousandths of the ultimate desired dimensions.

A group of these gears is then assembled.

upon a carrier 11 formed of a non-oxidizing material having a coefficient of expansion considerably lower than the coefiicient of expansion of the gear material and having splines 12 thereon which fit the splined portlon of the gears with such a degree of closeness that, when the carrier and its associated group of gears is subjected to the necessary heat treatment, the splined surfaces of the gears will be free to expand and contract under the heat treatment and such that when the heated group is projected into the quenching bath, say a cyanide bath, the flow of the bath into contact with the splined surfaces of the gears will be materially retarded although not entirely prevented.

In order to accomplish this result, I have found that satisfactory results may be'pro 4 duced by using a carrier of chrome-nickelalloy which has a very low coeflicient of expansion. This plug is conveniently provided atone end with a retaining flange 14 and at the other end with a perforation 15 through 4 which a sustaining hook may be projected.

Inoperation a group of the green gears I is placed upon the holder. The assembly is then subjected to the necessary heat treatment; and then, suspended from its perforated end, is lowered into the quenching bath. The quenching results in a hardening of the teeth of the gears to the desired extent and, because of the retarded quenching of the splined portions of the gears, due to the retarded flow of the bath to these portions and the heat of the holder, the splined surfaces of the gears, While hardened sufficiently to meet con'nncrcfal requirements of those portions of the gear, are not hardened to an extent equal to the teeth. The splined portions of the gears being free to expand and contract under the heat treatment, the teeth are not so distorted as they would be if the splinedportions were held against expansion and contraction and undesirable inter- 55 nal stresses are not set up within the bodies of the gears, and the splined portions come out of'the bath at a degree of hardness which permits a finishing broaching, which may be accomplished economically, so that the splined portions may be readily finished to the degree of accuracy required.

I claim as my invention:

- 1. The process of producing splined gears which comprises the formation of a gear of-a specified material with the splined surfaces thereof reduced closely to the desired dimensions, the placing of said gear upon a splined holder, the subjection of said holder and gear to a heat treatment, the subjection of the heated holder and the gear to a. quenching bath, and the subsequent removal of material "at the splined surfaces of the gear to reduce said surfaces to ultimate dimensions, the holder having such dimensions and such coeflicient of expansion that the splined surfaces of the gear will be free to expand and contract during heat treatment and such that the flow of quenching bath to said splined surfaces will be retarded but not ultimately prevented whereby the splined surfaces of the gear upon emergence from the quenching bath will be less hard than the teeth thereof, and in condition to permit, as by a broaching operation, the removal of material therefrom for a-final finishing operation.

' 2. The process of producing splined gears which comprises the formation of gears of a specified material with the splined surfaces thereof reduced closely to the desired dimen- 109 l0 gear will be free to expand and contract dursions, the placing of said gear upon a splined holder, the subjection of said holder and gear to a heat treatment, the subjection of the heated holder and gear to a quenching bath, and the subsequent removal of material at the splined surfaces of the gear to reduce said surfaces to ultimate dimensions, the holder being formed of non-oxidizing material and having, such dimensions and such coefiicient of expansion that the splined surfaces of the ing heat treatment and such that the flow of quenching bath to said splined surfaces will be retarded but not ultimately prevented whereby the splined surfaces of the gear blank, upon emergence from the quenching bath will be less hard than the teeth thereof and in condition to permit as by a broaching' operation, the removal of material therefrom for a final finishing operation.

In witness whereof, I, ERNEST F. DAVIS, have hereunto set my hand at Muncie, Indiana, this 30th day of J uly, A. D. one thousand nine hundred and thirty.

ERNEST F. DAVIS. 

